1. Field of the Invention
The present invention relates to a method of transferring a laminate. In addition, the present invention relates to a method of manufacturing a semiconductor device having a circuit structured by semiconductor elements, typically thin film transistors, in which an object to be peeled that contains the semiconductor elements is transferred to a substrate. For example, the present invention relates to an electro-optical device, typically a liquid crystal module, a light emitting device, typically an EL module, or an electronic device in which such a device is mounted as parts thereof.
2. Description of the Related Art
In recent years the focus has been on techniques of structuring thin film transistors by using semiconductor layers (having a thickness on the order of several nm to several hundreds of nm) formed on a substrate having an insulating surface. The thin film transistors are widely employed in electronic devices such as ICs and electro-optical devices, and in particular, the development of thin film transistors as switching elements of image display devices has been accelerating.
Many different kinds of applications that utilize this type of image display device have been anticipated, and the application to portable devices particularly has taken center stage. Devices that are lightweight, resistant to impact, and able to withstand some amount of deformation are expected. Glass and quartz are often used in thin film transistor substrates at present, and these substrates have disadvantages in that they are heavy and they easily break. Further, it is difficult to make large-size glass and quartz substrates, and therefore they are unsuited to thin film transistor substrates from the viewpoint of mass production. Trials have consequently been performed for forming thin film transistors on lightweight, durable plastic substrates, typically substrates having flexibility such as plastic films.
However, the present situation is that plastic has a low heat resistance, and therefore the maximum process temperature for forming the thin film transistors must be lowered. As a result, thin film transistors cannot be formed having electrical characteristics that are as good as those of thin film transistors formed on substrates having relatively high heat resistance, such as glass substrates, and quartz substrates.
On the other hand, peeling methods for peeling an object to be peeled, which exists on a substrate through a separation layer, from the substrate have already been proposed. For example, the techniques discussed in JP 10-125929 A (pages 4 to 10) and JP 10-125931 A (pages 6 to 10) are ones in which a separation layer made from amorphous silicon (or crystalline silicon) is formed, and air gaps are made to develop within the amorphous silicon (or the crystalline silicon) by passing laser light through a substrate and emitting hydrogen contained in the amorphous silicon. The substrate is then peeled from the object to be peeled.
In addition, processes similar to the techniques of JP 10-125929 A and JP 10-125931 A are reported in JP 2002-217391 A (pages 3 to 6, FIG. 9) for: forming a separation layer made from amorphous silicon (or crystalline silicon); forming a second substrate (temporary transferring member) on a surface of an object to be peeled (stated as layer to be peeled in the official gazette, typically indicating a thin film transistor) by using a water-soluble temporary adhesive layer; irradiating laser light to a separation interlayer insulating film through the substrate; peeling a first substrate (glass substrate) from the objet to be peeled, and transferring the object to be peeled onto a third substrate (film); immersing the third substrate within water, and dissolving the water-soluble temporary adhesive layer; and peeling the object to be peeled from the second substrate, thus exposing the surface of the object to be peeled.
However, it is essential to use a substrate having good light transmitting characteristics with the methods disclosed in JP 10-125929 A and JP 10-125931 A, and therefore there is a problem in that the substrates capable of being used are limited. Further, a relatively high-power laser light irradiation is necessary in order to impart an energy sufficient to pass through the substrate and cause hydrogen contained in the amorphous silicon to be emitted, and therefore there is a problem in that the laser light may damage the object to be peeled.
Further, if high-temperature heat treatment is performed in an element manufacturing process when manufacturing elements on the separation layer by the aforementioned methods, hydrogen contained in the separation layer diffuses and is reduced, and there is a concern that peeling cannot be sufficiently performed even if laser light is irradiated to the separation layer.
In addition, the transferring member is fixed to the surface of the object to be peeled using a curing adhesive, and therefore the surface of the object to be peeled, for example, the surface of the thin film transistor, specifically wirings or pixel electrodes are not exposed when peeling the substrate from the object to be peeled, and therefore it is difficult to measure the characteristics of the object to be peeled after peeling off the substrate. For cases of manufacturing a liquid crystal display device or a light emitting device using an object to be peeled with this type of structure, the structure becomes one in which a plurality of substrates are bonded to one another, and the thickness of the liquid crystal display device or the light emitting device becomes larger, and there is a problem in that electronic devices cannot be made smaller when using the liquid crystal display device or the light emitting device. Further, there is a problem in that projection light from a backlight in a liquid crystal display device, and light emitted from light emitting elements in a light emitting device each cannot be effectively taken out.
The object to be peeled and the second substrate are bonded by a water soluble adhesive in the invention disclosed in JP 2002-217391 A, but the surface area of the water soluble adhesive that is exposed to water is small in actuality, and therefore there is a problem in that peeling of the second substrate takes time.
In addressing this problem, it is possible to shorten the peeling time by removing a portion of the second substrate and exposing a much larger surface area of the temporary adhesive layer. The second substrate is disposable in this case, but there is a problem in that costs will increase when using expensive materials such as quartz glass, or rare materials in the second substrate.
In addition, if an organic resin is used in an interlayer insulating film of the thin film transistor, which is the object to be peeled, there is a problem in that the volume of the interlayer insulating film expands and the film deforms because organic resins tend to absorb moisture, and thin film transistor wirings will peel off.